1. Field of the Invention
The present invention relates to a lens apparatus, and more specifically to a lens apparatus capable of performing serial communication with a camera body.
2. Description of the Related Art
A lens apparatus loaded into a camera body of a television camera is normally provided with a parallel interface as a standard device so that various signals can be communicated between the camera body and the lens apparatus through the parallel interface. For example, a signal to be transmitted from the camera body to the lens apparatus can be a focus control signal for use in an autofocus operation, an iris control signal for use in an auto-iris operation. A signal to be transmitted from the lens apparatus to the camera body can be position information, etc. such as focus, zoom, iris, etc.
In the parallel interface, a predetermined type of signal is assigned as a transmission signal to each connector pin. Therefore, with greater variations of signals to be communicated between the camera body and the lens apparatus, the number of connector pins increases correspondingly. Practically, with increasing functions of a lens apparatus, the number of types of signals to be communicated between the camera body and the lens apparatus also increases. However, since the number of pins is limited, there have conventionally been a camera body and a lens apparatus capable of communicating various signals in serial communications (for example, Japanese Patent No. 3332808).
A camera body or a lens apparatus capable of performing serial communication is normally provided with a parallel interface in light of compatibility, and has the function of automatically switching between the serial communication and the parallel communication depending on whether the party is a serial communicative apparatus or not. Thus, when both camera body and lens apparatus can perform the serial communication, a signal is communicated in the serial communication. When one of them cannot perform the serial communication, the parallel communication can replace the serial communication for signals.
However, although both camera body and lens apparatus can perform serial communication, there can be a case in which no serial communication is required when the number of functions to be used is not so large. In fact, unnecessary information can bother a user when performing the serial communication, and cause trouble to an operation. Furthermore, when a large amount of information is communicated in the serial communication, a heavy load is put on a processing circuit (mainly the CPU) in the lens apparatus, which possibly reduces the throughput of the processes other than the communications. To compensate for this, the processing speed has to be enhanced with a high-speed clock, thereby requiring high power consumption.